A tubular expansion system and method are disclosed in US patent application No. 2013/312954 A. A well tubular is expanded by pulling an expansion cone therethrough and the outer surface of the well tubular comprises sealing rings for sealing the remaining annular space between the expanded well tubular and surrounding formation, which seals may leak if the wellbore has an irregular inner surface.
Downhole annular sealing systems are described in U.S. Pat. No. 3,857,736 and US patent application US2004/0182582, which sealing systems can only seal an annular space with a limited width.
There is a need to provide an improved annular seal around the bottom of an expandable liner which is activated by the expansion process and seals the annulus between the open hole and the expanded liner to prevent U-tubing of the liquid cement during expansion of the liner even if the wellbore has an irregular inner surface and/or in a wide annular space.